Permanent magnet holding device and mechanical detaching combination



13, 1959; J. SMIT EFAL 2,86

PERMANENT MAGNET HOLDING DEVICE AND MECHANICAL DETACHING COMBINATION Filed April 13, 1954 1 1 l'lwdimm'l :5 I 6 :4 4 7 ADRIAAN RADEMAKERS AGENT United States Patent PERMANENT MAGNET HOLDING DEVICE AND MECHANICAL DETACHING COMBINATION Jan Smit and Adriaan Rademakers, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application April 13, 1954, Serial No. 422,880 Claims priority, application Netherlands April 27, 1953 I 4 Claims. (Cl. 317159) The invention relates to a system comprising a holding magnet having at least one permanent magnet and a mechanical detaching device controlled by means of a set of levers and is characterisedin that a member is provided rotatable on a lever secured so as to be rotatable to the holding magnet, the line from the rotary axis of the lever to the rotary axis of the member extending, the discharging device being in its normal position, substantially in the direction in which the holding magnet is to be loosened from the load, the member extending at least substantially as far as the pole surface of the holding magnet.

The use of such a detaching device permits, exactly at the beginning of the detachment, of exerting the greatest force on the-load, since the operative lever arm acting upon the load is then extremely short and starts substantially at zero length. This is desirable, since exactly-at the beginning of the detachment the magnetic force is a maximum and decreases rapidly and considerably as soon as an air gap is formed between the pole surface of the magnet and the load.

The term holding magnet is to be understood to mean herein an adhering magnet, a magnetic jaw socket for holding pieces to be worked and, more particularly, a lifting magnet for lifting and transporting ferromagnetic work pieces, for example, iron sheets and the like by means of a hoisting crane.

The member is preferably constituted by a roller, the radius of which is at least substantially equal to the distance between the rotary axis of the roller and the pole surface of the lifting magnet. When the lever is actuated, only rolling friction occurs.

In order that the invention may be readily carried into elfect, it will now be described with reference to the accompanying drawing.

Fig. 1 is a lateral view of a magnetic jaw socket 1, to which a work piece 2 is attached. Two levers 3 are rotatable at 4 and provided on the side of the jaw socket. 011 the levers are seated rollers 5, the rotary axes of which are designated by 6. The rollers 5 just touch the work piece 2. The line from the point of rotation 4 to the rotary axis 6 extends in the direction in which the work piece is to be detached from the jaw socket. By moving a lever 3 (Fig. 2) to the left or to the right, the roller rolls over the work piece 2 and urges the jaw socket away from the work piece. Since the lever arm acting upon the workpiece increases substantially from zero, the force exerted on the work piece will be very great at the beginning, even if a small force is exerted on the lever 3.

By coupling the two levers 3 by means of pivotable intermediate members 7 with a lever 9 rotatable about a stationary shaft 8, the levers 3 may be controlled simultaneously by moving the handle 10 to the left or to the right.

In a similar manner two levers with rollers may be provided on the other parallel side of the jaw socket,

of the magnet having identical 2,869,047 Patented Jan. 13, 1959 these levers being coupled via the shaft 8 With the lever 9, so that the four levers 3 may be actuated simultaneously.

The size of the levers 3, of the distance between the points of rotation 4 and 6 and of the diameter of the rollers 5 varies with the requirements for the exerted forces and forces to be exerted and the height of elevation.

Instead of using the workpiece 2, use may be made of an intermediate plate 2, for example, of soft iron, serving as a pole plate with one or more pole shoes, so that even small work pieces 2 may be detached from the pole surface of the magnet.

Figs. 3 and 4 show a further embodiment which is particularly suitable for use as a lifting magnet. Corresponding parts are designated by the same reference numerals. However, the levers 3 are shaped in the form of an L and linked by pivotable intermediate pieces 11 and 12. By moving upwards the shaft 13 in the direction of the arrow 14, the load 2 is detached. The upward force may also be supplied by the hoisting crane by which the lifting magnet 1 is moved upwards. The dimensions are, in this case, such that the detaching force is smaller than the weight of the lifting magnet.

Fig. 5 shows a preferred construction of the holding magnet. It is formed by alternating strips of soft magnetic material 15 and permanent magnetic material 16. The material is made from non-cubic crystals of polyoxides of iron and at least one of the metals Ba, Sr, Pb and, if necessary, Ca, preferably a material, the ferromagnetic properties of which are mainly determined by single and/or mixed crystals of magnetoplumbite structure of the composition MO.6Fe O wherein M designates one of the metals Pb, Ba or Sr as disclosed in U. S. Patent No. 2,762,777 to Jan Jacobus Went et al. and U. S. Patent No. 2,762,778 to Everet Willem Gorter et al. This material has a particular advantage for the said purpose in that it is substantially not demagnetised and in that it has a high coercivity. The strips are magnetised in a manner such that the thickness of the strips is the direction of length poles at 17 and opposite poles at 18, so that the strips 19 also have identical poles and the strips 20 have opposite poles. The distance between two adjacent strips 15 is equal to the length of the magnet. The magnets should preferably be proportioned such that the strips 15 are almost saturated in the position of adhesion. Furthermore the maximum thickness 21 of the intermediate strips 15 is preferably determined by the thickness of the thinnest sheet to be lifted, in order to avoid that more than one sheet is lifted from the pile. The thickness 21 is then twice the thickness of the sheet, since the flux from one pole is distributed towards the other poles on either side thereof.

Fig. 6 is a cross sectional view of a more advantageous construction than that shown in Fig. 5. The sectional areas of the magnets 16 and the strips 15 of soft iron are trapezoidal. The active pole surface is designated by 25. Since the flux is at a maximum on the lower side of the strips 15 (here the lines of force from the two pole surfaces lying each on one side of the magnets 15 unite, see the broken lines) the sectional areas of the strips 15 are also at a maximum at this point.

Furthermore the distance between N- and S-poles of the magnets 16 is a maximum on the top side, so that on this side stray (see the broken lines) is reduced.

Fig. 7 finally shows a construction in which the roller is replaced by a member 22, provided so as to be rotatable at 6 on the lever 3. By way of the pivot 23 the member is coupled with the member 24, which urges the magnet 1, upon rotation of the lever 3 about the axis 4, away from the load 2.

If, as in the aforesaid case, use is again made of four levers, the members 24 may be united to form one piece surrounding the magnet 1.

What is claimed is:

1. A mechanical device for separating a workpiece from a pole face of a magnetic body comprising a lever arm rotatably attached to at least one side surface of said magnetic body for moving one end of said lever arm in a direction relative to the surface of said pole face, a roller rotatably attached at a point through the center thereof on said one end of said lever arm for initially engaging without pressure the surface of the workpiece adjacent to the pole face of said magnetic body, the point of attachment of said lever arm being nearer to said workpiece than the point of attachment of said roller, said lever arm upon movement describing at least a partial circular movement around the point of attachment of said roller whereby the roller exerts pressure on said workpiece and the latter is separated from the magnetic body by rolling engagement of the roller with said workpiece. 4

2. A mechanical device for separating a workpiece of a magnetic body as claimed in claim 1 in which a plurality of interconnected lever arms are mounted on the magnetic body for simultaneously moving an end of each of said lever arms toward and away from the workpiece; a plurality of rollers, each of said rollers being mounted on said one end of each of the corresponding lever arms adjacent the pole face.

3. A mechanical device for separating a workpiece from a pole face of a magnetic body having substantial- 1y parallel sides comprising means for lifting said magnetic body, two pairs of crossed lever arms rotatably attached on opposite sides of said body for moving an end of each of said lever arms in a direction toward the surface of said pole face, a plurality of rollers rotatably attached at a point through the center thereof on the end of each of said lever arms for initially engaging without pressure the workpiece on the pole face of said magnetic body, the point of attachment of each of said lever arms being nearer to said workpiece than the point of attachment of the adjacent roller, another pair of rotatably attached lever arms joining the other ends of each pair of crossed lever arms, means for actuating said rotatably attached lever arms which moves said crossed lever arms, each of said crossed lever arms upon actuation describing at least a partial circular movement around the point of attachment of each of said adjacent rollers whereby each of said rollers exerts pressure on the workpiece to separate the workpiece from the magnetic body by rolling engagement of each of said rollers with said workpiece, the actuating force applied to the actuating means being in the same direction as the force applied for lifting said magnetic body, and the detaching force applied to said lever arms being less than the weight of said magnetic body.

4. A mechanical device for separating a workpiece from a pole face of a magnetic body as claimed in claim 3 in which said magnetic body is constituted of alternate strips of magnetic and non-magnetic materials each having a trapezoidal cross-section, said magnetic materials being constituted of hexagonal crystals provided with a magnetoplumbite structure and having the composition MO.6Fe O wherein M is one of the metals selected from the group consisting of Ba, Sr, and Pb.

References Cited in the file of this patent UNITED STATES PATENTS 1,487,811 Savage Mar. 25, 1924 2,493,846 Andrews Jan. 10, 1950 FOREIGN PATENTS 569,251 Great Britain May 15, 1945 

